Electric vehicles in the prior art almost exclusively deploy inverters that take direct current (DC) power and voltage from one or more on-board batteries and convert that power to an alternating current (AC) voltage and power to drive different types of electric motors. These inverters are typically called “traction inverters” and consume most of the onboard battery power of the electric vehicle. An exemplary electrical inverter in the prior art is illustrated in FIG. 1.
Coexisting on present electric vehicles are charging devices that typically accept AC power and voltage from the electric utility grid and convert that power and voltage to DC power and voltage to charge the batteries while the vehicle is stationary. An exemplary electrical charger in the prior art is illustrated in FIG. 1. These types of chargers typically include a dual active bridge, an example of which is illustrated in FIG. 3.
The traction inverter and the charger operate independently, yet have very similar functionality, components and structures. Additionally, the traction inverter and the charger operate on the vehicle in a mutually exclusive manner, wherein one can only operate when the other one is not operating.
Past attempts at combining inverting and charging in a single device have proven that traction inverter and charger can be combined but either at the expense of charging efficiency or of costly methods involving the use of the traction motors with a winding inductance that interacts with the AC electrical power grid.
Attempts to use the same semiconductors that drive the electric motor to convert the AC power and voltage from the electric utility grid and charge the battery have proven that semiconductor losses, particularly switching losses—those losses incurred in the states between the off and on states and the on and off states of the semiconductor—are sufficiently high to make charging efficiency unacceptable under present industry requirements. Main cause is the primary design objective of the semiconductor, that is, providing sufficient current to drive the traction motor. Such current is usually 10 to 20 times the current required to charge the battery given typical AC level 1 and AC level 2 electric vehicle supply equipment (EVSE), which are prevalent in residential charging domains.
Because of the need for relatively high currents, presently used semiconductor packages consist of a number of paralleled insulated gate bipolar transistors (IGBT's). Each paralleled IGBT incurs losses as it transitions from a low loss off state to a low loss on state and, conversely, from a relatively low loss on state back to a low loss off state again every pulse width modulated (PWM) cycle.
The PWM frequency for driving the traction motor is relatively low in comparison to the PWM frequency of a typical active front end (AFE) deployed in a charger. The lower PWM frequency of use for a traction motor is due to the relatively low harmonic or passive losses incurred in the traction motor during operation and the need to keep switching losses relatively low in view of the overall losses incurred at the high currents required to propel the vehicle.
Conversely, the AFE of the charger requires higher switching frequencies to reduce the magnetics (inductors) required between the semiconductors of the active front end and the electric utility grid. Additionally, the charger requires about 1/20th to 1/10th of the current that is required of the traction motor and traction inverter.